Production of laminate filaments

ABSTRACT

DISCLOSED IS A PROCESS FOR PRODUCING LAMINATE FILAMENTS WHICH FIND SPECIAL UTILITY IN THE CONSTRUCTION OF ANTISTATIC FABRICS. A FIRST WEB FORMED OF POLYMERIC MATERIAL, E.G., POLYETHYLENE TEREPHTHALATE FILM, AND A TEARABLE SECOND WEB FORMED OF ELECTRICALLY CONDUCTIVE MATERIAL, E.G., ALUMINUM FOIL, ARE LAMINATED INTO A 2-PLY STRUCTURE WITH A STRING INTERPOSED BETWEEN THE PLIES IN A PATH WHICH TRA VERSES THE WIDTH OF THE STRUCTURE AT LEAST ONCE. THE STRING IS SUBSEQUENTLY TORN FROM THE STRUCTURE IN A MANNER WHICH FORMS IN THE ELECTRICALLY CONDUCTIVE PLY A VOID HAVING A CONFIGURATION COINCIDING WITH THE PATH PREVIOUSLY DESCRIBED BY THE STRING. THEREUPON THE LAMINATE IS SLIT IN THE DIRECTION OF ITS LENGTH FORMING LAMINATE FILAMENTS, EACH OF THE ELECTRICALLY CONDUCTIVE PLIES OF WHICH HAVING AT LEAST ONE DISCONTINUITY ALONG ITS LENGTH.

July 3, 1973 R. G. DUBY ET AL 3,743,559

PRODUCTION OF LAMINATE FILAMENTS Filed May 5, 1971 FIG. I

|NVENTORS= RUSSELL G. DUBY ROBERT E. EVANS JAMES A. GUSACK STERLING M. NICHOLS PETER J. SCHOOTS ROBERT E. SMELSER BERNARD B. STEPHENS THEIR ATTORNEY unitedsatesraem O 3,743,559 PRODUCTION OF LAMINATE FILAMENTS Russell G. Duby, Robert E. Evans, James A. Gusack, and

Sterling M. Nichols, Williamsburg, Peter J. Schoots,

Nieuwendam, and Robert E. Smelser and Bernard B.

Stephens, Newport News, Va., assignors to Dow Badische Company, Wiiliamshurg, Va.

Filed May 3, 1971, Ser. No. 139,330 Int. Cl. B32]: 5/00 U.S. Cl. 156-177 Claims ABSTRACT OF THE DISCLOSURE Disclosed is a process for producing laminate filaments which find special utility in the construction of antistatic fabrics.

A first web formed of polymeric material, e.g., polyethylene terephthalate film, and a tearable second web formed of electrically conductive material, e.g., aluminum foil, are laminated into a 2-ply structure with a string interposed between the plies in a path which traverses the width of the structure at least once. The string is subsequently torn from the structure in a manner which forms in the electrically conductive ply a void having a configuration coinciding with the path previously described by the string. Thereupon the laminate is slit in the direction of its length forming laminate filaments, each of the electrically conductive plies of which having at least one discontinuity along its length.

SUBJECT MATTER The present invention relates to textiles in general, and in particular to a process for producing laminate filaments which are used to construct antistatic fabrics.

PRIOR ART The accumulation of static electricity in humans as a result of their contact with fabrics is a phenomenon which has commanded the attention of the textile industry for some time, as the presence of static is not only a cause of annoyance, but also of danger.

Accordingly, many expedients have been proposed for avoiding the accumulation of high concentrations of static electricity. Of these, the most satisfactory, with respect to their efiiciency and permanence, are those which comprehend the utilization of fibers possessing electrical conductivity (especially metal fibers, and more advantageously, metallic laminate filaments) in combination with natural and/or man-made fibers to produce a woven, knitted, netted, tufted, or otherwise fabricated structure, the utilization of which prevents the build up of static electricity to undesirable levels. Some of the more noteworthy of these methods and structures may be found in US. Pats. 2,129,504; 2,714,569; 3,288,175; and 3,069,746; in Webber, Metal Fibers, Modern Textile Magazine, May 1966, pp. 72-75; and particularly in US. patent application Ser. No. 635,014, filed May 1, 1967.

That these expedients are efficacious in preventing the buildup of static electricity is not disputed. However, they have been found wanting in one most important aspect; viz, persons in contact with these metal-containing structures are not free of the hazard of electrocution. This hazard has been effectively removed by the invention in the copending US. patent application of C. E. LoWry, W. J. Gilbertson and I. A. Gusack for Laminate Filament and Fabric Prepared Therefrom, which application was filed on Nov. 27, 1790, Ser. No. 93,194. Specified and defined therein is a fabric which efiiciently and permanently avoids the accumulation of undesirable concentrations of static electricity While presenting no electrocution hazard, the fabric being prepared by standard ice fabricating procedures from novel laminate filaments possessing at least one polymeric ply bonded to a ply comprising an electrically conductive material having at least one discontinunity along its length.

However, production of these novel laminate filaments has been heretofore accomplished only with considerable technological difficulty. For example, in one prior method of producing these novel laminate filaments, a discontinuous adhesive layer is applied to one or both of the opposed surfaces of webs of selected polymeric film and metal foil, which materials are then laminated by means of heat and pressure, for example, in a continuous manner utilizing pairs of pressure rollers to bring the webs into intimate contact. The resulting laminate is then stretched to a degree sufficient to break the metallic layer in those areas where no adhesive is present, but insufficient to break the metallic layer in the relatively greater areas where adhesive, film, and foil are in intimate contact. Prior procedures such as this, which are time-consuming and/ or unprecise, do not readily result in a uniform product, and are, therefore not especially suitable for commercial exploitation.

SUMMARY OF THE PRESENT INVENTION Accordingly, it is an object of this invention to provide a rapid and precise process for preparing laminate filaments which comprise a polymeric ply bonded to an electrically conductive ply having at least one discontinuity along its length.

In accordance with the present invention, this advantage is achieved, and the disadvantages of the prior art processes are avoided, by the practice of a procedure which encompasses:

(a) Providing a first web formed of polymeric material and a tearable second web formed of electrically conductive material;

(b) Forming an adhesive coating on one surface of a web;

(0) Laying out upon a surface of a web a string in a path which traverses the width of the surface;

(d) Laminating the first and second webs, with the adhesive and laid-out string positioned therebetween, into a 2-ply structure;

(e) Tearing the string from the 2-ply laminate by exerting upon the string a force having a component in the direction 90 degrees from the surface of the electrically conductive ply; and

(f) Subsequently slitting the laminate in the direction of its length to form laminate filaments. As a result, each electrically conductive ply of every laminate filament has at least one discontinuity along its length.

A 3-ply laminate filament may be advantageously prepared according to the instant invention by (A) effecting the lamination of (1) a third web formed of polymeric material with (2) the 2-ply structure in (e) above, from which the string has been tom, the third web being adhesively bonded to the electrically conductive ply; and (B) BRIEF DESCRIPTION OF THE DRAWING For a more complete understanding of the present invention, reference should be made to the detailed description set forth below, which should be read together with the accompanying drawing, wherein:

FIG. 1, in schematic side elevation, depicts the first stage of a process in accordance with the present invention;

FIG. 2 illustrates the same process stage depicted in FIG. 1, as viewed from above; and

FIG. 3 is a diagrammatic side elevation showing the final stage of a process according to the present invention.

DETAILED DESCRIPTION With particular reference to the drawing, FIG. 1 shows a polymeric web 1A, to a surface of which an adhesive has been applied 4, being introduced into combining rolls 9, together with a tearable web of electrically conductive material 2 and a string 3. The combining rolls 9 may be heated, if desired, to cure the adhesive employed. The resulting 2-ply structure has the. string 3 interposed between the polymeric ply 1A and the electrically conductive ply 2.

FIG. 2 shows that the path of string 3 has been made to traverse the width of the 2-ply structure 5 at least once, the path actually shown being a wave whose amplitude equals the width of the structure 5.

FIG. 3 shows the string 3 being pulled from the 2-ply structure 5 at a right angle to the surface of the tearable electrically conductive ply 2, whence the 2-ply laminate from which the string has been removed is introduced into combining rolls together with a second polymeric web 1B, a surface of which has been coated with an adhesive 7. The resulting 3-ply structure 8, which comprises an electrically conductive ply 6 having at least one discontinuity along its length, is slit at 11 to form laminate filaments.

Polymeric webs used in the process of the present invention may be fabricated from any of the commonly employed filmor fiber-forming polymers by standard procedures very well known in the art. Thin sheets or films formed from cellulosics (e.g. cellulose butyrate), polyamides (e.g. nylon), polyolefins (e.g. crystalline polypropylene), and especially polyesters (e.g. polyethylene terephthalate) have been found to be useful. Polyethylene terephthalate film having a thickness of from 0.00025 to 0.00150 inch is deemed preferable. When two polymeric webs are employed to prepare a 3-ply structure, the polymeric webs may be composed of the same or different materials.

Tearable, electrically conductive webs employed in the process of the instant invention are advantageously very thin sheets or foils of a metal, such as copper, silver, nickel, chromium, lead, tin, aluminum, or alloys of these metals. Aluminum foil is preferred, because of its properties of high ductility, excellent electrical conductivity, and resistance to oxidative attack. Aluminum foil having a thickness of from 0.00025 to 0.00100 inch is most advantageously employed.

Adhesives having utility in this invention include natural and man-made thermoplastic resin composition of a sufiicient degree of tackiness, which compositions may include plasticizers and/ or inert, volatile diluents. Useful examples are the commercially available polyester adhesives, which are advantageously applied by roll applicators onto at least one surface of the webs which are to be bonded, until the surface has a substantially continuous adhesive coating of from 0.00005 to 0.00015 inch in thickness.

The string to be employed herein is any slender, continuous strip or line of round, fiat, or other desired cross section, as, for example, a filament, thread, yarn, cord, twine, wire, strand, band, ribbon, tape, or the like, among many others. Examples of highly satisfactory strings are spun cotton yarn and polyester cord having a diameter or width of from about 0.005 to about 0.100 inch. The resulting voids in the electrically conductive plies of the laminate filaments produced by the process of this invention are sufficient to block the passage of current available from an ordinary electrical outlet. (See the copending U.S. patent application of Lowry, Gilbertson, and Gusack, referred to above.)

The string may be coated with an adhesive before being positioned between the webs to be laminated, or it may be employed without any adhesive whatever. The path of the string positioned between the webs to be laminated should traverse the width of the electrically conductive web at least once, in order that at least one interruption or discontinuity in every electrically conductive ply will result when the laminated structure, from which the string has been subsequently torn, is ultimately slit along its length to form laminate filaments. Proper positioning is advantageously accomplished by laying the string upon the surface of a web which may be previously coated with adhesive, in such a manner that the path of the string describes a wave whose amplitude equals the width of the surface. In this manner the length of the wave will be equal to twice the average distance between interruptions in the electrically conductive plies of laminate filaments which are ultimately produced from the laminated structure by a slitting of the structure along its length. Wave lengths of from about 0.1 to about 10 feet are most conveniently and advantageously employed, and the corresponding average distance between interruptions in the electrically conductive plies of the laminate filaments ultimately produced results in a highly satisfactory product. (See the copending U.S. patent application, of Lowry, Gilbertson and Gusack, referred to above.).

Tearing of the string from the 2-ply laminate is accomplished by exerting on the string a force having a component in the direction degrees from the surface of the electrically conductive ply, and preferably by pulling the string from the laminate in a direction at approximately a right angle from the surface of the electrically conductive ply.

After the string has been torn from the 2-ply laminate, a third web formed of polymeric material may be adhesively bonded to the electrically conductive ply to form a 3-ply structure, which is subsequently slit along its length to produce laminate filaments having an electrically conductive ply and a polymeric ply bonded to each side thereof. Alternatively, the electrically conductive ply of the 2-ply laminate from which the string has been torn may be coated with a polymeric material before the structure is slit to produce laminate filaments. As another alternative, the Z-ply structure may be slit into filaments immediately after the string has been removed therefrom. The laminate filaments are wound onto spools for subsequent utilization in the production of antistatic fabrics.

EXAMPLE 1 Illustrated in this example is an embodiment of the process according to the present invention. A first web of polyethylene terephthalate having a thickness of 0.0005 inch was coated on one surface thereof which a commercial polyester adhesive (see U.S. Pat. 3,170,833) by means of a roll applicator. A substantially continuous adhesive coating of 0.00008 inch in thickness resulted. Onto a second tear-able web of aluminum foil having a thickness of 0.00045 inch was laid out a continuous cord (36 denier/ 16 filament polyester yarn core wrapped with cotton yarn) having a width of 0.01 inch. The cord was laid out upon the aluminum foil in a continuous path describing a sine wave having an amplitude equal to the width of the foil and a wave length of 6 feet. The two webs, with the adhesive-coated surface and the laid-out string positioned therebetween, were introduced into combining rolls at a temperature of 360 F. The resulting 2- ply structure, with the string interposed between the plies, was allowed to cool, whereupon the string was pulled therefrom at approximately a right angle to the surface of the electrically conductive ply, producing a void in the electrically conductive ply, which void coincided with the path previously described by the string. Simultaneously with the removal of the string, the 2-ply laminate was introduced into combining rolls at a temperature of 360 F., along with a third Web, formed of polyethylene terephthalate, a surface of which had been coated with a commercial polyester adhesive (see U.S. Pat. 3,170,833) by means of a roll applicator. The third web and the laminate were introduced into the combining rolls so that the third web was adhesively bonded to the electrically conductive ply of the laminate. The resulting 3-ply laminate was slit by means of rotary shear-type knives into filaments having a width of A inch, and the filaments were wound onto spools for subsequent utilization as metallic yarn.

EXAMPLE 2 This example, which is not illustrative of the present invention, is set forth for comparative purposes only. A sheet of aluminum 0.00045 inch thick was laminated to two sheets of polyethylene terephthalate, each of which was 0.0005 inch thick, employing a commercially available polyester adhesive (see U.S. Pat. 3,170,833) on each side of the aluminum. Instead of two continuous layers of adhesive, a discontinuous adhesive layer was applied to one side of the aluminum, each of the discontinuities therein being approximately 1 inch in length and having a width equal to the width of the aluminum surface. The average interval between discontinuities was 1.5 feet, all distances being measured along the length of the aluminum surface. After the adhesive had been cured, the 3- ply laminate Was slit into filaments having a width of inch, which filaments were then stretched to 40% of their original length and subsequently wound onto spools for utilization as metallic yarn.

Comparison of the filaments prepared by the process of Example 1 (this invention) with the filaments prepared by the process of Example 2 (prior process) indicated that the product of the present invention, in contradistinction to that of the prior process, is uniform; i.e., the interruptions in the metallic ply thereof are congruous, as determined, for example, by a measurement of the relative ease with which a potential of 200 volts D.C. could force a potentially lethal current across the individual interruptions.

Although the present invention has been described in detail with respect to certain specific and preferred embodiments, it is apparent to those having skill in this art that variations and modifications in this detail may be effected without any departure from the spirit and scope of the invention, which is defined in the hereto-appended claims.

What is claimed is:

1. A process for the production of a laminate filament, comprising:

(a) providing a first web formed of polymeric material and a tearable second web formed of electrically conductive material;

(b) forming an adhesive coating on one surface of a web;

(c) laying out upon a surface of a web a string in a path that traverses the width of the surface;

((1) laminating the first and second webs, with the adhesive and laid-out string positioned therebetween into a 2-ply structure;

(e) tearing the string from the 2-ply laminate by exerting upon the string a force having a component in the direction 90 degrees from the surface of the electrically conductive ply; and

(f) subsequently slitting the laminate in the direction of its length to form a laminate filament, each of the electrically conductive plies of which has a discontinuity along its length.

2. The process according to claim 1, wherein the string is laid out upon a surface so that the configuration of the string describes a wave having an amplitude equal to the width of the surface.

3. The process according to claim 2, wherein the wave length is between about 0.1 and 10 feet.

4. The process according to claim 1, wherein the electrically conductive web is a metal foil.

5. The process according to claim 4, wherein the metal is aluminum and polymeric web is polyethylene terephthalate film.

6. A process for the production of a laminate filament useful in the fabrication of antistatic structures, which process comprises:

(a) providing a first web formed of polymeric material and a tearable second web formed of electrically conductive material;

(b) forming an adhesive coating on one surface of a web;

(c) laying out upon a surface of a web a string in a path that traverses the width of the surface;

(d) laminating the first and second webs, with the adhesive and laid-out string positioned therebetween, into a 2-ply structure;

(e) tearing the string from the 2-ply laminate by exerting upon the string a force having a component in the direction degrees from the surface of the electrically conductive ply;

(f) effecting the lamination of (1) a third web formed of polymeric material with (2) the 2-ply structure from Which the string has been torn, the third web being adhesively bonded to the electrically conductive ply; and

(g) slitting the resulting 3-ply laminate in the direction of its length to form a laminate filament, each of the electrically conductive plies of which has a discontinuity along its length.

7. The process according to claim 6, wherein the string is laid out upon a surface so that the configuration of the string describes a wave having an amplitude equal to the width of the surface.

8. The process according to claim 7, wherein the wave length is between about 0.1 and 10 feet.

9. The process according to claim 6, wherein the electrically conductive web is a metal foil.

10. The process according to claim 9, wherein the metal is aluminum and the polymeric webs are polyethylene terephthalate film.

References Cited UNITED STATES PATENTS 2,829,701 4/1958 Keely 156-554 3,361,616 1/1968 Schart 156-250 530,678 12/1894- Bowers 156-248 I. TRAVIS BROWN, Primary Examiner J. L. GOODROW, Assistant Examiner U.S. Cl. X.R. 156-248 

